Very important; of high importance.
Necessary.
Necessary for survival but not synthesized by the organism, thus needing to be ingested.
Being in the basic form; showing its essence.
Really existing; existent.
Having the nature of essence; not physical.
Such that each complementary region is irreducible, the boundary of each complementary region is incompressible by disks and monogons in the complementary region, and no leaf is a sphere or a torus bounding a solid torus in the manifold.
Idiopathic.
A necessary ingredient.
A fundamental ingredient.
Essential; crucial; extremely important.
Having semantics that incorporates mutable variables.
Expressing a command; authoritatively or absolutely directive.
Of, or relating to the imperative mood.
A verb in imperative mood.
The grammatical mood expressing an order (see jussive). In English, the imperative form of a verb is the same as that of the bare infinitive.
An essential action, a must: something which is imperative.